1. Technical Field
The present invention relates generally to a method and apparatus for polishing semiconductor devices and in particular to a method and apparatus used in chemical mechanical polish processing for polishing wafers. Still more particularly, the present invention relates to a method and apparatus for conditioning a polishing pad used in chemical mechanical polishing processing.
2. Description of the Related Art
As circuit dimensions shrink, the need for fine-line lithography becomes more critical and the requirements for planarizing topography becomes very severe. Major U.S. semiconductor companies are actively pursuing Chemical-Mechanical Polishing (CMP) as the planarization technique used in the sub-half micron and below generation of chips. CMP is used for planarizing bare silicon wafers, interlevel dielectrics, metals, and other materials. CMP machines, such as the one shown in FIG. 1, use orbital, circular, lapping, and linear motions. The wafer 116 is held on a rotating carrier 118 while the face of the wafer 116 being polished is pressed against a resilient polishing pad 114 attached to a rotating platen disk 112. A slurry is used to chemically attack and lubricate the wafer surface to make the surface more easily removed by mechanical abrasion. Pad conditioning is done by mechanical abrasion of the pads 114 in order to `renew` the surface. During the polishing process, particles removed from the surface of the wafer 116 become embedded in the pores of the polishing pad 114 and must be removed. Current techniques use a conditioning head 122, also called a "grid", with abrasive diamond studs to mechanically abrade the pad 114 and remove particles to condition the polishing pad. Conditioning arm 124 positions conditioning head 122 over polishing pad 114.
The term "condition" defines the state of the polishing pad surface. The ideal surface of the polishing pad is free of embedded slurry particles and residual polished material. To provide a polishing surface, the condition is two fold. First, the mechanical action of the grid will clean the polishing pad of removed polished materials and old slurry particles embedded into the pad. Second, the abrasive surface of the grid will roughen the polishing pad and expose new pad surface for acceptance of slurry. These actions are used to provide a conditioned polishing pad. The repeated abrasive action of the conditioning will eventually erode enough material from the polishing pad to require replacement of the pad. The pad erosion from the conditioning can have an impact on the uniformity of the wafer. Also, if the slurry has a low pH, the acidic properties will erode metal grids and diamonds dislodged from the grid can cause severe scratching on the polished surface.
Therefore, it would be advantageous to have an improved method and apparatus to reduce the erosion of the polishing pad, enhance control of wafer nonuniformity, and allow the use of low pH solutions.